The present invention relates to a position control device of the type commonly referred to as a trackball device. Such devices are used, for example, to control the movement of a cursor of a video display, as in a video game.
Trackball devices include a housing having a circular opening therein and carrying a plurality of rotatable supports, at least two of which are respectively rotatable about orthogonally related axes. A ball is loosely seated on the supports with a portion of the ball projecting through the opening for access by a user, so that the user can manually rotate the ball. The rotatable supports respectively respond to the corresponding components of rotational movement of the ball. The orthogonally related supports are respectively connected to signal generating devices for producing signals indicative of the speed and direction of rotation of the supports. The two orthogonally related supports respectively correspond to the X and Y directions of movement of the cursor, so that the speed and direction of movement of the cursor in the X and Y directions correspond respectively to the speed and direction of rotation of the associated supports.
In prior trackball devices the axes of rotation of the supports are fixed, and proper operation of the device requires manufacture of the parts to very exacting tolerances. Thus, for example, the ball must not engage the housing lest it impede rotation thereof, yet the gap between the ball and the housing around the perimeter of the ball opening must not be too great, so as to avoid pinching of the user's fingers between the ball and the housing. Manufacture of the trackball device to the required tolerances is quite costly, since it precludes the use of certain inexpensive materials and fabrication techniques.
Furthermore, prior trackball devices have tended to be unduly rattly and have exhibited poor shock and impact resistance.